The present invention is generally directed to ophthalmic lenses and, in particular, to progressive multifocal ophthalmic lenses which include a far vision viewing zone, a near vision viewing zone and an intermediate zone which smoothly blends the far vision viewing zone into the near vision viewing zone.
Each of the different viewing zones in progressive multifocal ophthalmic lenses are of different power for properly viewing objects at different distances. The refractive surface of such lenses are aspherical which inevitably causes a large amount of astigmatism and distortion. Accordingly, attempts have been made to design the refractive surface of such lenses in order to improve the characteristics thereof and reduce the astigmatism and distortion. U.S. Pat. Nos. 3,687,528, 3,910,691 and 4,056,311 disclose various constructions for progressive multifocal ophthalmic lenses. Moreover, the present inventor has also invented several previous constructions for progressive multifocal ophthalmic lenses which are disclosed in co-pending U.S. patent application Ser. No. 327,288, filed Dec. 3, 1981 now U.S. Pat. No. 4,580,883.
Lenses of the type described above are constructed to improve the curved lens surface in respective regions of the lens. However, zone of these lenses or the patents in which they are described recognize that it is important in designing lenses to consider the optical efficiency and appearance of the lens, that is, considering a base curve (a curve of a refractive surface in the far vision viewing zone on the basis of which the curved surfaces in other zones are determined) and the prescribed power. If the base curve and prescribed power are not in satisfying condition with respect to each other, the appearance of the lens is less than completely satisfactory and, also, in the case where a lens of strong power is prescribed, the optical efficiency of the lens is deteriorated.
The present invention is directed to improved progressive multifocal ophthalmic lenses wherein the problems discussed above are substantially overcome or eliminated.